1. Field of the Invention
The present invention relates to an active-matrix type liquid crystal display device and manufacturing method thereof. More particularly, the present invention relates to an active-matrix type liquid crystal display device of CF on TFT structure of forming both a switching element such as TFT (Thin Film Transistor) and so forth and CF (color filter) on the same substrate and its manufacturing method.
2. Description of the Related Art
Recently, development of active-matrix type liquid crystal display device of using thin film transistor and so forth as switching element is advanced. The active-matrix type liquid crystal display device is composed of TFT substrate on which switching element such as thin film transistor and so forth are formed, opposed substrate on which opposed electrode is formed, and liquid crystal put between these substrates. The TFT substrate has thin film transistor consisting of gate electrode, gate insulating film, semiconductor layer, and source/drain electrode, pixel electrode formed in every pixel, passivation film covering them, orientation film, and terminals for connecting external circuit, and so forth. In addition, the opposed substrate has black matrix for interrupting incident light heading toward thin film transistor area and wiring layer, color filter of each color of RGB (Red, Green and Blue) of conducting color display, transparent electrode made from ITO (Indium Tin Oxide) and so forth and orientation film and so forth. Further, spacers for keeping gap between both substrates by predetermined distances are put between both substrates.
About such active-matrix type liquid crystal display device, in order to improve display appearance quality, high precision fine display is required. For that reason, it is necessary to achieve pixel with high density. However, in the liquid crystal display device of structure, in which above described color filter and black matrix are arranged at the side of opposed substrate, since error occurs on position matching between both substrates in assembly process, it is necessary to form color filter and black matrix somewhat largely in anticipation of margin beforehand. For that reason, it is difficult to make rate of area of opening section to area of pixel large, namely it is difficult to make opening rate large, thus it becomes obstruction for the pixel with high density.
Accordingly, in order to improve opening rate while reducing margin of color filter and black matrix, method for forming color filter and black matrix at TFT substrate side of forming switching element such as thin film transistor and so forth, so called CF on TFT is proposed. For instance, Japanese Patent Application Laid-Open No. Hei 2-54217 and Japanese Patent Application Laid-Open No. Hei 3-237432 disclose CF on TFT.
In CF on TFT, since color filter and black matrix are formed on the TFT substrate, it is unnecessary to take into consideration position matching margin between the TFT substrate and the opposed substrate. Accordingly, it is possible to simplify manufacturing process and it is possible to achieve improvement of opening rate of pixel.
However, in CF on TFT, since pixel electrode is formed on color filter, step occurs at pixel electrode while reflecting unevenness of color filter and so forth. Then, disturbance occurs in orientation of liquid crystal caused by the step, so, there is the problem that the step causes defects such as disclination and reverse tilt domain and so forth.
In order to solve the problem, Japanese Patent Application Laid-Open No. Hei 8-122824 discloses method for forming flattened film after conducting patterning of color filter and black matrix in order to fill unevenness of color filter and black matrix. FIG. 1 is a sectional view illustrating configuration of conventional CF on TFT described in Japanese Patent Application Laid-Open No. Hei 8-122824. It should be noted that the Japanese Patent Application Laid-Open No. Hei 8-122824 discloses technique of using polycrystal silicon TFT (p-Si TFT) as switching element, however, in the present specification, for convenience of explanation, explanation is made that channel-etch type amorphous silicon TFT (a-Si TFT) is used as switching element.
As illustrated in FIG. 1, in liquid crystal display device described in the Japanese Patent Application Laid-Open No. Hei 8-122824, a gate electrode 5b is formed on a transparent insulative substrate 4a, and a gate insulator 6 is formed so as to cover the gate electrode 5b. A semiconductor layer 15 is formed so as to overlap a gate electrode 5b with several times over on the gate insulator 6. In addition, a source electrode 8b and a drain electrode 8a separated on the center section of the gate electrode 5b are connected to the semiconductor layer 15 through an ohmic contact layer (not illustrated), thus thin film transistor is formed. Further, a passivation film 9 is formed so as to cover the thin film transistor.
In the liquid crystal display device of CF on TFT structure, a color filter 10 and black matrix 11 are formed on the passivation film 9, and a pixel electrode 14 is formed thereon through the overcoat layer. In the liquid crystal display device illustrated in FIG. 1, in order to flatten step formed by the color filter 10 and the black matrix 11, a flattening film of thick film 24 is provided. For this measure, it is characterized in that the color filter 10 and the black matrix 11 are made to embed completely in the flattening film 24. In addition, a contact hole 19 of penetrating the flattening film 24 and the passivation film 9 is formed, after that, the pixel electrode 14 made of transparent conductive film is formed, and the pixel electrode 14 is connected to the source electrode 8b. 
On the other hand, an opposed electrode 16 is formed on surface of the transparent insulative substrate 4b that stands opposite to the transparent insulative substrate 4a. In addition, liquid crystal 3 is filled between the transparent insulative substrate 4a and the transparent insulative substrate 4b. 
In formation process of CF on TFT substrate, it becomes necessary to form fine pattern of black matrix with high light shielding characteristic of degree of Optical Density (OD)=3 made of photosensitive resin as light shielding film of thin film transistor. It should be noted that OD is value defined as OD=xe2x88x92log10(T1/T0) when incident amount of light into black matrix is taken to be T0, and amount of projected light is taken to be T1. In this configuration, when black matrix is made to execute exposure, neighborhood of surface of black matrix is only executed exposure, so there is the problem that adhesion to base section becomes low.
Japanese Patent Application Laid-Open No. 2000-013571 discloses technique for forming fine pattern in such a way as to conduct exposure while providing photoconductive resin black matrix on color filter to be base section. According to this method, even though only surface neighborhood of high-OD black matrix layer is executed exposure, since adhesion is good between color filter to be base section and black matrix layer, it is possible to form fine pattern without separating black matrix from the base section.
However, there are problems indicated below in the above-described conventional technique. According to flattening technique described above, the flattening film 24 is applied so as to cover a step formed at TFT substrate. Generally, film thickness of the black matrix 11 and the color filter 10 is degree of 1 to 2 xcexcm, thus step of degree of 2 to 3 xcexcm is created when the black matrix 11 and the color filter 10 are overlapped. Accordingly, when the step is made to cover by the flattening film 24, film thickness of degree of 1.5 times the step becomes necessary, so, film thickness of degree of 3 to 4.5 xcexcm is necessary as the flattening film 24. As a result, film thickness of the flattening film 24 becomes thick.
When photoconductive type acrylic resin as material of the flattening film 24, in particular, positive type photoconductive acrylic resin is used, since transmittance of light in the neighborhood of wavelength of 400 to 500 nm in this acrylic resin is degree of 95% in every film thickness 1 xcexcm, transmittance of the whole flattening film 24 with film thickness of 3 xcexcm becomes degree of 85%. For that reason, problem occurs in which transmittance of light in the liquid crystal display device deteriorates, and/or white balance collapses. Thus, since effective transmittance becomes low caused by thick film of the flattening film 24, step of the color filter 10 and the black matrix 11 is not flattened completely, but disclination created by the step is made to execute light shielding by using black matrix, so, on the contrary, in some cases, effective transmittance becomes high.
On the other hand, when no flattening film 24 is provided completely, the color filter 10 and the black matrix 11 are subjected to swelling by remover and so forth used at patterning process to create release from end section. In addition, if thin film made of acrylic material and so forth identical with the flattening film 24 is made to form on the color filter 10 and the black matrix 11, so that only overcoat layer is made to form thereon, following problems occur. Generally, overcoat layer is applied by using spin coat method. However, since step of the color filter 10 and the black matrix 11 is extremely large, it is next to impossible to apply overcoat layer to area in which the step is large on surface of the color filter 10 and the black matrix 11. For that reason, in process after forming overcoat layer, for instance, in resist exfoliation process in pixel electrode formation process, defect occurs such that black matrix is subjected to swelling to create release from end section.
As described above, as for liquid crystal display device of CF on TFT structure, it is possible to improve opening rate while reducing margin of position matching between TFT substrate and opposed substrate, however, large step occurs caused by color filter and black matrix on surface of TFT substrate. When forming thick flattening film for filling the step, light transmittance of TFT substrate lowers because flattening film absorbs light, thus there is the problem that effect of opening rate improvement is cancelled out.
It is an object of the present invention to provide an active-matrix type liquid crystal display device of CF on TFT structure and its manufacturing method capable of protecting color filter and black matrix surely without reducing transmittance. In addition, it is another object of the present invention to provide an active-matrix type liquid crystal display device and its manufacturing method capable of obtaining gap between TFT substrate and opposed substrate in high precision and simply without providing spacer specifically.
An active-matrix type liquid crystal display device according to the present invention comprises first and second transparent substrates being arranged opposite to each other, a plurality of gate lines and data lines formed on a surface of the first transparent substrate being in opposite state to the second transparent substrate, in which the gate lines and the data lines cross mutually, a thin film transistor, provided at the surface of the first transparent substrate, in which the gate line is connected to its gate electrode and the data line is connected to its one of source/drain electrode thereof, a color filter which is provided, at least, at pixel area, which is an area surrounded by said gate line and said data line except both transistor formation area on which said thin film transistor is formed and data line formation area on which said data line is formed, an overcoat layer which is provided in such a way as to cover at least end section of both the thin film transistor and the color filter. The overcoat layer comprises a thin film part which is formed, at least, on the pixel area, and a thick film part which is formed on the transistor formation area or formed on both the transistor formation area and the data line formation area, in which film thickness of the thick film part is thicker than film thickness of the thin film part. The active-matrix type liquid crystal display device further comprises a pixel electrode which is provided at the pixel area, in which the pixel electrode is connected to the other of the source/drain electrode, an opposed electrode which is provided at surface of the second transparent substrate being in opposite state to the first transparent substrate, and liquid crystal which is provided between the first transparent substrate and the second transparent substrate.
In the present invention, overcoat layer consists of thin film part and thick film part. Then, the thick film part is arranged at transistor formation area, whereby it is possible to protect surely constituted subject in the transistor formation area, and it is possible to improve transmittance of the light in such a way as to arrange thin film part on pixel area.
In addition, it is possible to obtain large distance between data line and pixel electrode in such a way as to arrange thick film part of the overcoat layer on data formation area. For this configuration, it is possible to reduce coupling capacitance between data line and pixel electrode, so that it is possible to improve display quality.
The overcoat layer may be formed from first overcoat layer and second overcoat layer, in which the thin film part consists of only the second overcoat layer and the thick film part is formed in such a way as to pile the first overcoat layer up the second overcoat layer. Further, the first overcoat layer may have an opening section in the pixel area, the color filter may be formed within the opening section, and the second overcoat layer may be formed on the first overcoat layer and on the color filter.
By this configuration, the color filter and the first overcoat layer are not overlapped with each other, thus it is possible to control creation of step at end section of color filter. As a result, display quality of liquid crystal display device is improved.
The active-matrix type liquid crystal display device may have spacers between convex section which is formed with both the thin film transistor and the thick film part of overcoat layer contained, and the opposed electrode. By this configuration, it is possible to use the first overcoat layer as the spacer while utilizing positively, so that height of columnar spacer of forming thereon can be made to lessen. As a result, it is possible to prevent defect in which columnar spacer collapses, thus it is possible to control gap between the first transparent substrate and the second transparent substrate in high precision and simply.
The convex section formed with both the thin film transistor and the thick film part of overcoat layer contained may come into contact with the opposed electrode. By this configuration, it is possible to eliminate process for forming columnar spacer.
A manufacturing method of active-matrix type liquid crystal display device which according to the present invention, comprises the steps of: forming a plurality of gate lines and data lines crossed mutually on a surface of a first transparent substrate, forming a thin film transistor on the surface, in which its gate electrode is connected to the gate line and one of its source/drain electrode is connected to the data line, forming color filter at least on pixel area, which is an area surrounded by said gate line and said data line except both transistor formation area on which said thin film transistor is formed and data line formation area on which said data line is formed, forming overcoat layer so as to cover at least end section of both the thin film transistor and the color filter in which its thin film part is arranged on at least the pixel area and in which its thick film part whose film thickness is thicker than film thickness of the thin film part is arranged on the transistor formation area or on both the transistor formation area and the data line formation area, forming the pixel electrode connected to the other of the source/drain electrode on the pixel area, forming opposed electrode on surface of a second transparent substrate, arranging the first transparent substrate and the second transparent substrate so that a surface of the first transparent substrate on which the thin film transistor is formed and a surface of the second transparent substrate on which the opposed electrode is formed are opposed each other, and filling liquid crystal between the first transparent substrate and the second transparent substrate.
In addition, the step of forming the overcoat layer may have the steps of forming selectively first overcoat layer, and forming selectively second overcoat layer, in which the step of forming the overcoat layer forms only the second overcoat layer on the thin film part and forms both the first overcoat layer and the second overcoat layer on the thick film part. Further, each of the steps of forming selectively the first overcoat layer and forming selectively the second overcoat layer may have the steps of forming application film while applying application material by using spin application method, and conducting patterning of this application film, in which the viscosity of application material of forming the second overcoat layer is lower than that of application material of forming the first overcoat layer. Or, each of the steps of forming selectively the first overcoat layer and forming selectively the second overcoat layer may have steps of forming application film while applying application material by using spin application method, and conducting patterning of this application film, in which number of spin revolution in step of forming the second overcoat layer increases than number of spin revolution in step of forming the first overcoat layer. By these methods, it is possible to form overcoat layer provided with thick film part and thin film part with simple method.
Further, the step of forming the overcoat layer may have steps of forming application layer, executing exposure of the application layer in such a way that amount of exposure is made to differ in every part, and executing patterning of the application layer in such a way as to remove the application layer selectively while executing development of the application layer and for forming thick film part and thin film part. Furthermore, the step for executing exposure of the application layer in such a way that amount of exposure is made to differ in every part while using masks have light shielding section, half-transmission section, and transmission section. By these methods, it is possible to form overcoat layer provided with thick film part and thin film part by one time execution of application, exposure and development.
Another manufacturing method of active-matrix type liquid crystal display device which comprises the steps of: forming a plurality of gate lines and data lines crossed each other on a surface of a first transparent substrate, forming a thin film transistor on the surface, in which its gate electrode is connected to the gate line and one of its source/drain electrode is connected to the data line, forming first overcoat layer at both transistor formation area on which the thin film transistor is formed and data line formation area on which the data line is formed in an area surrounded by the gate line and the data line, forming color filter at least on pixel area, which is an area surrounded by said gate line and said data line except both transistor formation area on which said thin film transistor is formed and data line formation area on which said data line is formed, forming second overcoat layer so as to cover at least end section of both the thin film transistor and the color filter, forming pixel electrode connected to the other of the source/drain electrode on the pixel area, forming opposed electrode on surface of a second transparent substrate, arranging the first transparent substrate and the second transparent substrate so that a surface of the first transparent substrate on which the thin film transistor is formed and a surface of the second transparent substrate on which the opposed electrode is formed are opposed each other, and filling liquid crystal between the first transparent substrate and the second transparent substrate.